1. Field of the Invention
The invention relates generally to tunneling magnetoresistance (TMR) devices, and more particularly to a TMR read head with an improved seed layer and free ferromagnetic layer/capping layer structure that enables a reduction in the read gap thickness.
2. Description of the Related Art
A tunneling magnetoresistance (TMR) device, also called a magnetic tunneling junction (MTJ) device, is comprised of two ferromagnetic layers separated by a thin insulating tunneling barrier layer. The barrier layer is typically made of a metallic oxide, typically MgO, that is so sufficiently thin that quantum-mechanical tunneling of charge carriers occurs between the two ferromagnetic layers. This quantum-mechanical tunneling process is electron spin dependent, which means that an electrical resistance measured when applying a sense current across the junction depends on the spin-dependent electronic properties of the ferromagnetic and barrier layers, and is a function of the relative orientation of the magnetizations of the two ferromagnetic layers. The magnetization of the first ferromagnetic layer is designed to be pinned, while the magnetization of the second ferromagnetic layer is designed to be free to rotate in response to external magnetic fields. The relative orientation of their magnetizations varies with the external magnetic field, thus resulting in change in the electrical resistance.
The TMR device is usable as a TMR read head in magnetic recording disk drives. The linear density of the bits in the data tracks of the disk is dependent on the along-the-track dimension of the TMR read head. Thus it is desirable to make this dimension, also called the read gap, as small as possible, but without a loss in magnetoresistance (AR/R) and designed magnetic properties, so that the read head can detect smaller-sized bits and still maintain the reading performance.